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I’m charging a Li-ion 3.7 V, 3500 mAh using a TP4056 charge controller IC and feeding a 6 V, 9 W monocrystalline solar panel to charge it.

When I connect the solar panel at good sun light at 2 PM in the noon, though what ever the programmable resistor I connect Rprog, 1k, 2k, 3k or 4.7k, the 4056 IC is heating very badly, at times my skin got peel off. What is the mistake we are doing?enter image description here

Shiv
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As @winny says, there is no place for the heat to go without a heat sink, so the temperature will rise. This device detects its own junction temperature, and will automatically reduce its output current to maintain the junction temperature at 145 Celsius. So with no heat sink, the chip will reach this temperature regardless of Rprog.

John Birckhead
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  • Thank you for this explanation. Could it get dangerours for the charged LiPo battery if they share the same case? If yes, what could one do to prevent it? – Helyon Jan 14 '21 at 18:01
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    If you are not in contact with the battery, I wouldn't worry too much. The thermal resistance of junction-to-case is not listed on the data sheet, but if you aren't attached to a heat sink you are probably going to shut down when you get a few watts dissipated in the part. The part also has a thermistor on it that you can use to monitor temperature and reduce power if you are worried about the battery overheating. – John Birckhead Jan 14 '21 at 21:53
  • Okay nice, thank you again for this good explanation! I think having some air between the battery should do the trick. – Helyon Jan 15 '21 at 00:03